This application claims the priority of German Patent No. 101 10 822.2-13, filed Mar. 7, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and a device for influencing the transfer of vibrations of a vibration generator to an object connected to it, in particular of engine vibrations to the body of a motor vehicle, as they occur for example in an automobile.
To change the vibrations emanating from a vehicle, in particular the noises which can be perceived in the passenger compartment, many measures have been taken, such as the use of various damping materials in the form of damping mats and the like as well as acoustic measures described below. The same of course applies to any object, such as machines which are connected to an object, for example, a floor or the hull of a submarine, etc.
U.S. Pat. No. 5,332,061 discloses a method for suppressing vibrations introduced into the vehicle body and a corresponding vehicle. The vibrations originate from the engine and are transferred at least indirectly via the engine supports to the vehicle body at the connecting points of the engine. To damp these vibrations, the vehicle has actuators designed as shakers (mechanical vibration exciters), which are arranged in the region of connecting points of the engine to the vehicle body. When the engine is operated, depending on the engine speed, the shakers are excited at the resonant frequencies in phase opposition to the vibrations coming from the engine, thereby damping the transfer of the vibrations. The frequencies and amplitudes of these secondary vibrations are taken from a previously recorded data.
U.S. Pat. No. 5,434,783 discloses a vehicle in which the audible noises within a passenger compartment are influenced by sound waves. In addition to the normal loudspeakers, a piezo element is used which induces the vehicle body to vibrate at least in certain regions and thereby influences the emission of sound waves. The piezo element functions as the coil of a loudspeaker, while the vehicle body functions as the vibrating diaphragm. With this method and this device, an improvement in the subjective perception within the passenger compartment is achieved.
A further refinement of the above development for influencing the subjectively perceived impression of driving is known from DE 195 31 402 A1. According to this document, both the air-borne sound and the structure-borne sound or vibrations perceived by the human body are influenced on the basis of one or more parameters, such as engine speed and vehicle velocity. For this purpose, certain data are obtained from a data field according to the sizes of the parameters and are converted with the assistance of vibration exciters into secondary vibrations, including secondary vibrations which can be perceived by the human body. Using these measures it is possible in combination with the influencing of the acoustically perceived air-borne sound to generate both positive and negative interferences of the artificial secondary vibrations with the primary vibrations forming on the vehicle side when the vehicle is in operation. The interferences can, as desired, reduce the perceived impression or simulate a certain impression, such as a gear change in a vehicle provided with a continuously variable transmission. However, the measures mentioned above are quite complex. Furthermore, they always require the use of weight-increasing damping mats made of a damping material.
The object of the invention is to develop a method and a device which make it possible to influence favorably and inexpensively noises and vibrations generated by a vibration generator, in particular an engine, to an object connected to it, in particular a passenger compartment of a vehicle.
The object is achieved according to the invention by a method and by a device described hereinafter. Two measures make it possible in a simple and inexpensive way to intervene efficiently in the transfer of vibrations which are introduced by a vibration exciter (in particular by an engine) via an intermediate element (in particular an engine support) into an object connected to it, in particular a vehicle body, and consequently into the passenger compartment. First, an actuator (for example, a piezo element) arranged on the exciter side can generate controlled vibrations, and second, a detector arranged on the object side can detect residual vibration. The control system comprises the intermediate element and also the detector and the actuator, which are arranged at the opposite ends of the intermediate element. Although the opposing arrangement of the detector and the actuator is seemingly less favourable from production engineering and design aspects, and consequently also from the cost side, it is unexpectedly technically successful.
Surprisingly, the arrangement according to the invention produces a frequency-dependent magnification factor and a frequency-dependent phase shift that facilitates the reduction of noise and/or vibration and/or an unwanted noise and/or vibration pattern (sound design), to an unexpected degree and also produce an easier control algorithm for vibration damping and/or a desired sound design.
This is of particular advantage since an engine is a solid component and consequently acts as a quasi-fixed supporting body for the piezo actuator. The inert engine block forms a virtual fixed point for the engine support or the vehicle body, which can be induced to undergo vibrations easily and with little energy. The detector, on the other hand, is arranged in a region of the acoustically softer object, since even low-energy excitations lead to relatively easily measurable excitation amplitudes.
The excitable piezo actuator and the detector, preferably likewise designed as a piezo element, can have a simple configuration such as an underlay shim and/or packing shim. As a result, one of the effects of the invention is to save costs, due for example to the simplification of the design requirements, to simplified component geometries, consequently cost saving in casting etc., and to a possible reduction in sound-damping measures, such as damping mats and the like.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.